Butadiene acrylonitrile copolymer sof-



modulus and tensile properties.

Reissued Nov. 11, 1958 Howard K. Nason, St. Louis, Mo., assignor to Monsanto Chemical Company,- St. Louis, Mo.,- a corporation of Delaware No Drawing. Original No. 2,820,018, dated January 14,

1958, Serial No. 555,227, December 27, 1955. Application for reissue March 3, 1958, Serial No. 718,937.

'3 Claims. (Cl. 260=31.8)

Matter enclosed in heavy brackets I: appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to the softening or plasticizing of synthetic rubber-like substances and is particularly concerned with copolymers of 1,3-butadiene and acrylonitrile.

The copolymers of butadiene-l,3 and acrylonitrile are resistant to oils and solvents, consequently these rubberlike substances find use where such property is essential. By the same token they are resistant to the ordinary type plasticizers and being tough and hard, cannot be satisfactorily processed on rubber mills or Banbury mixers without suitable processing aids. Another shortcoming, since the vulcanized products are generally used in contact with fuels, oils or other solvent materials, is that the plasticizer is often leached out and lost, thereby contaminating the fluid and detracting from the rubbery properties of the copolymer.

A primary object of this invention is to' provide a new class of softeners or plasticizers compatible with rubbery copolymers of butadiene-1,3 and acrylonitrile. A further object is to provide a class of materials which render the copolymers soft and easily processed so that the addition of compounding and curing agents is facilitated. A still further object is to provide a class of softeners which enable the preparation of vulcanizates having desirable A further particular object of the invention is to provide a class of plasticizers which resist extraction from the butadiene-l,3-acrylo- 'nitrile copolymers.

It has now been found that these and other objects are achieved by incorporating liquid addition polymers of alkyl acrylates and certain chain terminating agents into rubbery copolymers of butadiene-l,3 and acrylonitrile. More particularly, addition copolymers consisting of one molecule of a copolymer of an alkyl ester or acrylic or methacrylic acid with to 50 mole percent of acrylonitrile or methacrylonitrile and one molecule of a chain terminating agent consisting of polyhalomethane dispersed quickly into butadiene1,3-acrylonitrile copolymer rubber -with which they appear miscible, plasticize the rubber efiiciently yet provide vulcanizates possessing high modulus and tensile properties from which the plasticizer cannot be extracted. The optimum range of acrylonitrile increases the pasticizer becomes more fluid. Acrylic acid rnay be substituted by methacrylic acid, the effect of employing esters of the latter being to decrease the fluidity of the plasticizer.

The new plasticizers of the present invention are conveniently prepared by a controlled polymerization tech nique whereby the chain terminating agent is actually a significant part of the molecule, which type polymer is known as a telomer. For example carbon tetrachloride is a suitable chain terminating agent, the chlorine being attached to one end of the chain and the -CCl group at the other. Increasing the ratio of chain terminating agent has the effect of lowering the molecular weight. For example ratios of carbon tetrachloride to total monomer of 2:1 have resulted in a plastiCizer compdsition having a molecular weight of about 5500. With a 4:1 ratio the molecular weight was about 4500 and when a 10:1 ratio was employed the molecular weight was about 2500. Polyhalomethanes in which the halogen is chlorine or bromine such as chloroform, bronioform, bromotrichloromethane and carbon tetrabromide are desirable constituents of the plasticizer and are efiicient chain terminating agents. Other chain terminating agents are useful but yield less efiicient plasticizers. Examples comprise compounds having active methylene groups such as toluene, ethyl benzene, cumene and other alkyl benzenes having a labile alpha hydrogen atom; the nitro alkanes as for example 2-nitro propane, and mercaptans, examples of which are ethyl mercaptan, propyl mercap tan, butyl mercaptan, hexyl mercaptan and dodecyl mercaptan. The proportion of monomer tomercaptan should be at least 5 to 1 by weight and may be as high as 1,000 to 1. However, an excess of chain terminating agent with respect to the total monomers present is preferred in the other cases mentioned. The presence of solvents or diluents is optional.

The reactions are promoted by polymerization catalysts for which purpose agents which liberate free radicals may be employed. These include peroxygen type compounds for example, acyl peroxides such as acetyl, benzoyl, lauroyl or stearoyl peroxides; hydrocarbon peroxides and hydroperoxides such as di-tert. butyl peroxide, cumene hydroperoxide, inorganic per-compounds such as hydrogen peroxide, potassium persulfate; hydrazine derivatives such as hydrazine hydrochloride and organometallic compounds such as tetra ethyl lead. In addition to the methods mentioned above for-controlling the molecular weight, the catalyst also exerts an influence as does the temperature of polymerization. Thus it is well known that increasing the polymerization catalyst tends to decrease themolecular weight as does increasing the temperature of polymerization. In general, the catalyst will be 0.1%5.0% of the total monomers although quantities up to 10% may be used.

A typical example of the new plasticizing agents is prepared by charging into a suitable reaction vessel parts by weight of butyl acrylate, 20 parts by weight of acrylonitrile, 400 parts by weight of carbon tetrachloride and 5% on the monomer of benzoyl peroxide. The mass is heated and stirred at refluxing temperature (88 C.) for six hours and the solvent removed. The residual liquid polymer constitutes a valuable plasticizing agent as hereinafter described. It was a heavy viscous liquid, M. W. 4500, very compatible with butadiene-acrylonitrile rubber and gave stocks which extruded smoothly and swelled very little after forcing through an orifice. The sheer plasticity was very low.

Further examples of the new plasticizers are listed below. These products were prepared by copolymerizing butyl acrylate and acrylonitrile (Nos. 1 to 10 inclusive) or methacrylonitrile (Nos. 11 to 14) in the mole ratio indicated. The plasticizers are addition polymers in which the polyhalomethane is a significant part of the molecule. The polyhalomethane was carbon tetrachloride except for No. where chloroform was used. Reaction was effected by heating and stirring 48 hours at 95 C.

Further details of the preparation are described in co-- Moles Aerylate Mole Ratio Per- Benzoyl and cent Butyl Acry- Peroxide, Chlorine, Nitrogen, nitrile late/Acrylonitrile Percent Percent Percent combined M. W.

or Methaeryloof Monoper mole nitrile mers of Polyhalomethane N 1 I 2 2. 89 2. 95 33.1 No 280/20 5 3.71 2.58 32.7 No 3-70/30 2 2.04 4.52 66.2 No 4-70/30. 5 2.86 4. 17 46.2 No 560/40 2 2.13 6.02 67. 5 No 6B0/20. 5 2.08 7.03 72.0 No 790/l0. 5 3.94 1.30 28.8 No 8-80/20- 5 3.80 No 80/20 5 3. 52 2. 32. 0 No 1080/20 0.005 1. 12 2. 86 84. 5 N0 1190/10 5 1.42 0.99 80.0 No 1280/20 5 2.65 2. 14 44.4 5,352 No 1370/30 5 1.81 3.81 70.1 7,835 No 1460/40 5 1.96 6.21 70.6 7,236

In general the efficient plasticizers contain 25 to 100 moles total of ester and nitrile combined with one mole of the polyhalomethane compound.

As illustrative of the plasticizing action the adduct of carbon tetrachloride and the copolymer of 80 parts by weight of 'butyl acrylate and 20 parts by weight of acrylonitrile described above was incorporated in a base stock containing the butadiene-acrylonitrile copolymer known by the trade name Hycar OR-15. Similar stocks were prepared containing other addition polymers. A synthetic rubber =base formula was compounded comprising Parts by weigh 'Hycar 0R-15 100.0 'Carbon black 60.0 Zinc oxide 5.0 Stearic acid 1.0 Sulfur 1.5 2,2'-dithiobis benzothiazole 1.5

The plasticizcr was added to the stock by milling in the usual manner and the plasticity of the stocks determined with several different types of plastometer. The Mooney plastometer which measures shear resistance is described by Melvin Mooney in Industrial and Engineering Chemistry, Analytical Edition, March 15, 1934, pages 147-151. The determination is carried out at 100 C., reading being taken after 4 minutes running in accordance with A. S. T. M. D92749T. The extrusion resistance was determined by means of a Firestone plastometer as described by I. H. Dillon in Rubber Chemistry and Technology, vol. 9, pages 496-501 (1936). The data recorded were obtained employing 10 pounds air pressure per square inch,.the stocks being extruded at 82 C. after 18 minutes preheating at 90 C. Plasticity was also determined -by means of a Williams plastometer as described by Williams in Industrial and Engineering Chemistry, vol. 16, page 362 (1924)-see alsoKrall, ibid., page 922. The test was run in accordance with A. S. T. M. D924- 47T. Samples of the stocks were preheated in a 70 oven for 18 minutes and the readings taken after 3 and 5 minutes and the plastometer at 70 F. The Williams plasticity is in reality the height of a rubber cylinder in ,5 mm. after the upper movable plate has rested upon 4 it for the prescribed time. The data reported are the average after 3 and 5 minutes.

Stock Plasticizer None.

80 Butyl acrylate and 20 aerylonitrile polymerized in 2- nitro propane.

Butyl aerylate polymerized in G014.

Butyl acrylate polymerized in OHC13.

80 Butyl acrylate and 20 acrylonitrile polymerized in G014.

Butylt aerylatepolymer terminated by tert. butyl mercap an.

Butyl acrylatepolymer terminated by tert. dodecyl mercaptan.

Butyl acrylate polymerized in toluene.

Tributoxyeethyl phosphate.

Plastlcizer Amount Mooney Firestone, Williams N 0. Seconds N 0.

none 130 200+ 177 20 58 183 130 30 31 55 119 20 46 128 30 36 32 113 20 50 26 132 30 35 25 123 20 20 118 119 30 18 133 114 20 36 16 122 20 36 15 20 36 14 132 20 44 96 93 In addition the stocks so compounded were vulcanized in the usual manner by heating in a press for 60 minutes at C. The resistance of the vulcanizates to solvent extraction was determined in accordance with A. S. T. M. D481-49T employing SR-6 solvent which is a hydrocarbon solvent corresponding to Reference Fuel #2 composed of 60% by volume di-isobutylene, 5% benzene, 20% toluene, 15% xylene, all of which conform to a certain standard and contains in addition 0.2 pound inhibitor per 1000 gallons of fuel. The stress-strain of the vulcanizates together with the percent weight extracted after 48 and 96 hours at 70 C. is set forth below:v

. Ultimate Percent By Weight Amount, Modulus Ultimate Elonga- Extracted Stock Parts at 300%, Tensile, tion,

by Wt. lbs/in. lbs/in. percent 48 hrs/70 96 hrs. [70

none 3, 280 3, 280 300 3. 5 1. 0

The properties of the E stocks are outstanding. The plasticizer used in these stocks was also very compatible with natural rubber. The addition of 20 parts to 100 parts of rubber on a mill required 12 minutes as compared to 24 minutes required to mix the same amount of a liquid copolymer of Z-ethylhexylacrylate 70% and butyl acrylate 30% prepared in kerosene. The long hydrophobic group in 'ethylhexylacrylate would be expected to impart high compatibility with hydrocarbon rubher but even here the polyhalomethane adducts are more soluble. These adducts are also soluble in most common organic solvents including the solvent mixture used for making the solvent extraction tests described above. From the resistance to extraction of these soluble plasticizers from butadiene-acrylonitrile copolynier rubber, reaction with the rubber must be postulated.

Butadiene-l,3-acrylonitrile polymers which contain in addition other polymerized constituents such as styrene, cyanobutadiene and esters of acrylic acid may be softened or milled with the new plasticizing agents. A relatively small amount exerts appreciable activity. As little as 1 part on the rubber may be employed although better results are obtained with -30 parts on the rubber.

It is intended to cover all changes and modifications of the examples of the invention herein chosen for purposes of disclosure which do not constitute departures from the spirit and scope of the invention.

range of 2,000-10,000 consisting of an addition polymer.

of one molecule of a copolymer of an alkyl ester of an acid selected from the group consisting of acrylic acid and methacrylic acid with 10 to 50 mole percent of a nitrile selected from the group consisting of acrylonitrile and methacrylonitrile and one molecule of a chain terminating agent consisting of polyhalomethane prepared by copolymerizing one molecular proportion of said ester with [0.1-0.5] 0.11-1.00 molecular proportion of said nitrile in the presence of the said chain terminating agent the moles thereof exceeding the total moles of monomer present, the chain terminating agent containing at least three halogen atoms selected from the group consisting of chlorine and bromine. r

2. A vulcanized plasticized rubbery copolymer of butadiene and acrylonitrile characterized by high resistance to hydrocarbon solvents comprising butadiene-1,3- acrylonitrile copolymerrubber in admixture with a liquid plasticizer polymer having a molecular weight within the range of 4,000-6,000 consisting of an addition polymer of one molecule of a copolymer of a lower alkyl ester of acrylic acid with 20 to mole percent of acrylonitrile and one molecule of a chain terminating agent consisting of polyhalomethane prepared by copolymerizing one molecular proportion of said ester with [02-04] 0.25-0.66 molecular proportion of acrylonitrile in the presence of said chain terminating agent, the moles thereof exceeding the'total moles of monomer present, the chain terminating agent having at least three chlorine atoms attached to a single carbon atom.

3. A vulcanized plasticized rubbery copolymer of butadiene and acrylonitrile characterized by high resistance to hydrocarbon solvents comprising butadiene-1,3- acrylonitrile copolymer rubber in admixture with a liquid plasticizer polymer having a molecular Weight within the range of 2,00010,000 consisting of an addition polymer of one molecule of a copolymer of butylacrylate and 20 to 40 mole percent of acrylonitrile and one molecule of carbon tetrachloride prepared by copolymerizing one molecular proportion of butylacrylate with [0.2-0.4] 0.25-0.66 molecular proportion of acrylonitrile in the presence of carbon tetrachloride, the moles of carbon tetrachloride exceeding the total moles of monomer.

No references cited. 

